Cationic dyes and uses thereof

This application is the § 371 U.S. National Stage of International Application No. PCT/EP2023/050579, filed 11 Jan. 2023, which claims the priority to European App. No. EP22305027.9, filed 12 Jan. 2022.

The present invention relates to new nanocellulose-based cationic dyes, to a process for their synthesis, and to their use in processes for dyeing fibers, in particular textile fibers.

The growth of human population and the current way of life have created an increasing demand for the consumption of clothing, amplifying the needs of textile dyeing.

Textile dyeing processes are generally energy-consuming, requiring long reaction times and/or the use of high temperatures, and create massive and often toxic effluents.

Dyeing of cotton fibers has been mainly performed over the past decades with reactive dyes, because such dyes are cost-effective and produce a wide range of colors. These dyes typically comprise aromatic chromophores and amine auxochromes, which give the color properties of the dye. They further comprise reactive groups, such as chlorine leaving groups, which afford linking the dye to the fabric surface via covalent bonds. Reactive dyes offer a very strong dye-textile fixation and excellent dyeing properties. However, chlorine ions are released during the chemical reaction, resulting in chloride-containing wastewater and colored sewage. In addition, reactive dyeing requires high thermal energy and pretreatment with salt saturated solutions to suppress the repulsive forces between the negatively charged dye molecules and cotton fibers. Electrolytes, such as sodium chloride, sodium carbonate and sodium sulphate, are added to the dyeing bath to improve the interactions between the dye and the fabric. Electrolyte concentrations are increased gradually to promote dye exhaustion which produce highly concentrated wastewater with a COD value equal to 50,000 ppm.

Mordant dyes may also be used for dyeing cotton fibers. Natural dyes, also referred to as direct dyes, are derived from natural sources as animals and plants, hence they are more environmentally friendly than reactive dyes. However, they do not form strong covalent bond with cotton surfaces. They bind to the cellulosic fiber via electrostatic bonds, weak Van der Waals forces and/or hydrogen bonds. To increase the affinity of natural dyes, metal mordants are used as a dyeing pretreatment. Mordants bind to the fabric and to the dye by strong coordination bonds, thus fixing the dye molecules to the fabric surface. Previously, toxic chromium, iodine, cobalt and/or nickel complexes were used as mordants. Recently, metals with lower toxicity such as copper, iron, and aluminum are adopted as a greener pretreatment product. However, the problem of excessive metals concentration in wastewater and the enormous volume of water needed persists. Natural bio-mordants could also be used as a green replacement for metal mordants. For example, whey protein, a mixture of three proteins of bovine serum albumin, was used to improve the affinity of pomegranate natural dye toward cotton via hydrogen bonds and to decrease negative charges repulsive forces between fabric and dye molecules. Unfortunately, such products are not widely used in industry because of their cost of production.

A few processes aiming at reducing the environmental impact of cotton fiber dyeing processes have been developed in the recent years.

Anuradhi Liyanapathiranage et al. “Nanocellulose-based sustainable dyeing of cotton textiles with minimized water pollution”2020, 5, 16, p. 9196-9203 disclose a dyeing process of cotton fibers using reactive dyes incorporated onto pristine nanocellulose fibers containing hemicellulose. The dying process is performed at 60° C. for 90 min, and a salt is used to create an affinity between the dye and the fiber. To further improve the fixation and lower the hydrophilic character, a post-treatment with polycarboxylic acids such as citric acid or maleic acid is performed, implying a soaking of the fabric in the solution and a drying step at a high temperature of 120° C.

Smriti et al. “Environment-friendly nanocellulose-indigo dyeing of textiles”2021, 23, p. 7937 disclose a dyeing process of cotton fibers involving a dye comprising natural indigo incorporated on nanocellulose fibers. The nanocellulose fibers dispersion is mixed with agglomerated indigo and a surfactant, Triton® X-100. The obtained suspension is mixed with cotton fibers, and a drying step is performed at 120° C. In order for the dyeing to resist washing of the cotton fabrics, a post-treatment involving chitosan solution adsorption is necessary. Said post-treatment is performed by soaking the dyed cotton fabrics with chitosan for 15 minutes, followed by a drying step performed at 120° C.

CN113914124 discloses a modified nanocellulose and its use for the preparation of base paper with improved mechanical properties. The modified nanocellulose is compounded with titanium dioxide and can be used as addition product to the base paper pulp.

CN105080503 discloses a nanocellulose polyvinylamine microgel and its use for absorbing dyestuff material in waste water, especially anionic dyes and heavy metal ions. The nanocellulose polyvinylamine microgel is not simultaneously cationic and colored: When the dispersion medium is acidic, the amine moiety is chelated to the anionic dyes, resulting in a material which is not cationic. When the dispersion medium is neutral or basic, the amine moiety is not cationic.

US2013/0211308 discloses nanosilver coated nanocellulose and its use for the manufacture of medical devices or antibacterial clothes. The material results from oxidation of nanocellulose to form aldehyde functions, followed by a Shiff reaction of an amine group with the aldehydes. The resulting material is not cationic

Document Cellulose (2015) 22:2443-2456 discloses amino functionalized nanocrystalline cellulose (ANCC) as an adsorbent for anionic dyes in waste water treatment. ANCC is not simultaneously cationic and colored.

Document Molecules, 2021, 26, 7315 discloses amino functionalized nanocrystalline cellulose and its use for the adsorption and removal of cations and anions from wastewater. The amino functionalized nanocrystalline cellulose is not simultaneously cationic and colored.

U.S. Pat. No. 9,506,187 discloses a method for dyeing textiles using a dyed nanocellulose dispersion. The nanocellulose bears no cationic moieties, only colored moieties. The dyeing method requires heating the dying bath to 80° C. and uses salts.

The document Materials, 2019, 12, 3144 discloses functionalization of cellulose nanofibrils with chitosan. Carboxyl and aldehyde groups are introduced on viscose backbone by an oxidation treatment based on TEMPO. The resulting textiles show antibacterial properties with improved resistance to washing cycles.

There thus remains a need for the development of new dyes, which would be suitable for implementing efficient dyeing processes of fibers, for instance textile fibers, such as cotton fibers, allowing an efficient fixation of the dye to the fibers, preferably without the need of a post-treatment, requiring as low energy consumption as possible, for instance by using only low temperatures, and limiting the production of effluents both in terms of volume and of toxicity, so as to limit the necessary retreatment of effluents.

The Applicant surprisingly evidenced that the use of a very specific dye comprising both a colored moiety and a cationic moiety linked to specific positions on the glycosidic rings of nanocellulose allows a very efficient dyeing of fibers, such as textile fibers. The dyeing processes using said dye afford among other advantages an improved fastness of the color, a reduced dyeing time and/or a reduced energy-consumption.

This invention thus relates to a cationic dye comprising:

In favorite embodiments, the cationic moiety and the colored moiety are linked to distinct carbon atoms of the nanocellulose backbone.

In some embodiments, the cationic moiety is covalently linked to nanocellulose in C2 and/or C3 position(s) of at least one glucose moiety of said nanocellulose.

In some embodiments, the colored moiety is linked with ionic and/or hydrogen bonds to nanocellulose in C6 position of at least one glucose moiety of said nanocellulose.

In some embodiments, the nanocellulose is selected from the group consisting of cellulose nanofibers, cellulose nanocrystals and any mixture thereof, preferably the nanocellulose is cellulose nanocrystals.

In some embodiments, the at least one cationic moiety comprises a quaternized amine group, preferably a quaternized primary amine group.

In some embodiments, the at least one cationic moiety is selected from the group consisting of a quaternized diamine moiety, a quaternized amino acid, a quaternized peptide and a quaternized protein.

In some embodiments, the colored moiety is a colored mineral moiety.

In some embodiments, the colored moiety is a metal or a metal oxide.

In some embodiments, the colored mineral moiety is iron oxide.

In preferred embodiments of the method for the synthesis of the cationic dye, the colored moiety is introduced as a precursor

In preferred embodiments, at least one cationic moiety and at least one colored organic or mineral moiety are different moieties in the cationic dye.

The invention further relates to a process for the synthesis of the cationic dye according to the invention, comprising the following steps:

The invention further relates to a process for the synthesis of the cationic dye according to the invention, comprising the following steps:

In an embodiment, the method for the synthesis of the cationic dye comprises a step of oxidizing at least part of the OH groups of optionally modified nanocellulose into aldehyde moieties.

In a favorite embodiment of the method for the synthesis of the cationic dye, NaIOis used for oxidizing at least part of the OH groups of optionally modified nanocellulose into aldehyde moieties.

The invention further relates to a process for dyeing at least part of a fiber material, comprising the steps of:

In some embodiments, the fiber material is a textile fiber material.

In some embodiments, the textile fiber material is selected from the group consisting of a cotton fiber material, a polyester fiber material, a keratinic fiber material and a mixture thereof.

In some favorite embodiments, the dyeing step is implemented at a temperature of 20° C. to 50° C., more preferably from 20° C. to 30° C.

In some favorite embodiments, the dyeing step is implemented in the absence of salts.

In some embodiments, the oxidant is selected from the group consisting of TEMPO, TEMPO in presence of iron, potassium hydrogenopersulfate, hydrogen peroxide, hydrogen peroxide in presence of iron (preferably an iron cation), and sodium metabisulfite.

In some embodiments, the process for dyeing at least part of a fiber material further comprises, after step b), a step of:

In the present invention, the following terms have the following meanings:

“About”, before a figure or number, refers to plus or minus 10%, preferably plus or minus 5%, more preferably plus or minus 1%, of the face value of that figure or number.

A “cationic moiety” is a moiety bearing at least one positive charge in the experimental conditions to which the cationic moiety is submitted, preferably in the experimental conditions used for the dyeing process.

A “cationic dye” is a dye bearing at least one positive charge in the experimental conditions to which the cationic dye is submitted, preferably in the experimental conditions used for the dyeing process.

“Cellulose nanocrystals”, also referred to as CNC, are crystalline nanostructures substantially consisting of cellulose molecules. CNC exhibit elongated crystalline rod-like shapes with a very limited flexibility compared to cellulose nanofibers as they do not contain amorphous regions. CNC are also known as nanowhiskers, nanorods, and rod-like cellulose crystals. They are usually isolated from cellulose fibers through acid hydrolysis. CNC possess a relatively low aspect ratio; they present a typical diameter of 2-20 nm and wide length distribution from 100 to 600 nm.

“Cellulose nanofibers”, also referred to as CNF, are nanoscale fibers substantially consisting of cellulose molecules. CNF have a diameter of about 3 nm and lengths in the micron scale and show both crystalline and amorphous sections. CNF may be prepared by means of TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxy)-mediated oxidation of cellulose, followed by mechanical treatment with a homogenizer.

A “colored moiety” is a moiety that is colored by itself, and/or that imparts color to the dye when it is bound to the nanocellulose. The colored moiety is preferably bound to the nanocellulose via ionic and/or hydrogen bonds. The colored moiety comprised in the dye according to the invention may be obtained through the binding of a precursor thereof, such as Fe, to the nanocellulose, and then the formation of the colored moiety, preferably iron oxide, in-situ from the precursor.

“Covalent”, when used to qualify a bond or a fixation, refers to the characteristic of a bond between two atoms resulting from the pooling of electrons coming separately from each of them. According to the present invention, a covalent binding of two moieties may be a binding of said two moieties through a linker moiety, that is covalently bound to each moiety. A linker moiety may be an atom or a chain of covalently linked atoms.

A “dye” refers to a natural or synthetic substance used to add a color to or change the color of a fiber material, in particular a textile fiber material.